The fibrogenic effect of asbestos may be caused by the physical and the chemical properties of the fibers. It is generally thought that the health effect is primarily dependent on the length of fibers within a specific range of fiber diameter. Past studies on the health effects of fibers have primarily been performed with ball-milled fibers of a wide diameter and length distribution having crystalline structures which are potentially very different from those actually occurring in the ambient environment. The reported effect may therefore not be due to the measured mean physical properties of the fibers. It is proposed that under the sponsorship of this grant a new technique will be tested and perfected which is hoped to classify fibers by length and diameter. The technique will continuously classify fibers in the airborne state thus making this technique available not only for intratracheal injection of milligran quantities, but also for gram-quantity dispersion of fibers for inhalation experiments. During the first year of the grant for which renewal is sought a complex fiber generation and classification system has been designed and constructed which will classify fibers by diameter through application of aerodynamic forces using the new opposing-jet classification procedure developed by the principal investigator, and will classify fibers by length through application of electrostatic forces, based on the principle that long fibers can sustain more electrostatic charges and can therefore be subjected to larger electrostatic forces. Additional size classification is sought through aerosolizing the fibers in a fluidized bed which exhibits classification characteristics upon mechanical and fluid-dynamic excitation. Fibers of glass and of different asbestos types which have been subjected to such classification procedures will be tested for their ability to induce pulmonary proline hydroxylase activity, as a measure of their fibrogenicity, and their ability to stimulate gastrointestinal DNA synthesis, as a measure of their genotoxicity towards cells in that tissue.